I'm probably in the same boat here. At my school, telling someone you want to get a 50 in a subject literally seems impossible. I have no idea why - but I'm out to prove a few people wrong. Thankfully, I've been doing really well in both my year 11 and 12 subjects and I want to be a doctor and get into Med. I really do believe that its mind over matter - don't let what people think of you or what the expectation is put you down. My school gets great results, but very rarely a student hits the 45+ in a subject like Biology, Chemistry or Physics for instance. But just because that hasn't happened, doesn't mean you can't make it happen.
Believe in yourself - because remember that those that tell you that you can't, and those who say that you wont, are those whom are petrified that you will!